


Sex Ed

by Destielshipper4Cas



Category: Supernatural
Genre: Alpha Dean, Alpha/Beta/Omega Dynamics, Barebacking, Bottom Castiel (Supernatural), Bottom Castiel/Top Dean Winchester, Explicit Sexual Content, First Time, Friends to Lovers, Getting Together, Knotting, Loss of Virginity, M/M, Omega Castiel, Omega Verse, Roommates, Smut, Top Dean Winchester, Virgin Castiel (Supernatural), Virginity Kink
Language: English
Status: Completed
Published: 2019-12-22
Updated: 2020-01-15
Packaged: 2021-02-25 23:20:45
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 4,174
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21903634
Author URL: https://archiveofourown.org/users/Destielshipper4Cas/pseuds/Destielshipper4Cas
Summary: Cas grew up in a religious family who have kept him sheltered all his life. When he finally gets out of there, his knowledge about sex is seriously lacking.Luckily, his alpha roommate Dean knows all about sex and can teach him a thing or two.It would be so much easier if feelings weren’t involved…
Relationships: Castiel/Dean Winchester
Comments: 131
Kudos: 1602





	1. Chapter 1

Cas had been open about his past from the beginning. When they had first moved in together, he had explained about his family and why he had severed all ties with them.

The omega had used words like ‘sheltered life’ and ‘religious family,’ but what it really boiled down to sounded more like ‘cult’ to Dean.

In any case, Cas had been homeschooled, and sex ed had not been part of his curriculum. The only things that had been drilled into him were ‘no sex before mating’ and ‘contraception is sin.’ So basically, once he was mated, he was supposed to pop out as many pups as possible.

That’s how Dean fell into the position of having to explain to Cas how pups were made at an age at which everyone was supposed to know all about these things.

They were sitting on Dean’s bed after they had watched a movie together, which had left Cas rather confused. Dean was showing him all kinds of movies because apparently, in Cas’ family, TVs were considered things of the devil, so they had a lot to catch up on. It usually led to Cas asking lots and lots of questions about things his family had tried to keep from him.

“So anyway, the knot ensures that the sperm stays inside the omega’s ass so that the chances of conception are better,” Dean finished.

How had they stumbled upon that topic again? Oh yeah, Cas had no idea of what was appropriate for roommates to discuss and had flat-out _asked_ after the movie had hinted at the alpha doing things to the omega.

Since Cas didn’t understand the concept of boundaries, Dean really shouldn’t have been surprised when, after his eyes had gotten rounder and rounder during Dean’s explanation, Cas looked straight into his eyes and asked in his usual deadpan, “May I see your penis?”

Dean did what every self-respecting alpha would in that situation and spluttered, “What? _No!_ What?!”

So, it remained a mystery why, five minutes later, he had his pants and underwear down around his ankles and his dick out. Cas had a way of getting what he wanted where Dean was concerned. Saying no to the cute omega sure seemed impossible sometimes, especially when he was looking at Dean all intense and asking for something.

Okay, so maybe Dean _did_ know how Cas had worn him down. With a shrug, he had offered, “You can see my ass when it’s producing slick, too.”

Of course, Dean had seen omegas’ asses slicking plenty of times before, whenever he was about to mount one. Still, he had found himself saying, “Okay,” and here they were.

Now, as Cas was peering at Dean’s dick, eyes narrowed, Dean wished he would have been able to stand firm.

“Where’s the knot?” Cas finally asked, accusatory, as if he thought Dean had given him false information. “It looks just like mine.”

Dean snorted at that. “Of course there’s no knot right _now_. I have to be aroused to pop one.”

He might have forgotten to mention that, but come on! _Every_ one knew that. Surely Cas was—

“Whaaaat are you doing?” Dean squeaked when Cas reached over to touch his dick.

“I have one of _those_ ,” Cas said, emphasizing his point by stroking Dean’s dick once, and oh, dear Lord, what was happening? Dean squeezed his eyes shut. “I want to see the _knot_ ,” Cas continued.

“Yeah, I don’t think that’s a great idea,” Dean said, trying in vain to compose himself. Despite what he was saying, he found himself rocking into Cas’ grip.

Oh, who was he kidding? It wasn’t like he would say no to Cas touching him in intimate places.

He might have fantasized about this, imagining it was Cas he was fucking into when he was with other omegas, or even when he was just beating off.

It was probably just the scent of virgin omega that was intriguing to him. Yeah, probably didn’t have anything to do with how much fun Cas was to be around or how making him laugh was making Dean’s chest feel tight and the rest of him tingly and giddy.

Cas’ touch was clumsy—he had never touched an alpha there before, after all—but it was _Cas_ , so Dean was fully erect in no time anyway.

Popping a knot didn’t always happen, especially when he wasn’t buried in an omega’s wet channel, so he was surprised when his knot began to form far more quickly than usual.

Cas realized what was happening, too, and slowed his strokes until he was just holding Dean’s dick. Then he scrutinized the knot, making Dean feel a bit self-conscious.

“That is so strange,” Cas said and poked at the knot.

“ _Yes_!” Dean panted. “Be careful,” he added because he was the one who knew all about sex, and Cas had no idea what he was in for.

Cas finally looked away from Dean’s knot and into his eyes to ask, “Or what?”

“Or I’ll come all over you.” Cas didn’t seem deterred by that, but rather intrigued, so Dean quickly said, “Your turn.”

He had been promised a slicking ass after all.

Cas let go of Dean’s dick, which immediately felt neglected, and got rid of his own pants.

Dean licked his lips when the omega laid down on his back and started fingering himself. Oh, he so shouldn’t take advantage of Cas’ naivety, but somehow, his eyes were fixed on Cas’ finger disappearing in his own hole, and it was all he could do not to join the action and finger Cas himself.

Cas’ own eyes were fixed on Dean’s cock and knot.

“We fit together like puzzle pieces,” Cas realized.

Dean was confused, aroused, and breathless, so answering anything at all was hard enough. He got out, “Uhm… Yeah. That’s how it’s supposed to work.”

He had seen countless assholes slick, but none had ever awakened these… these urges inside of him. Sex was just something he did to get his mind off of things. It was fun. Easy. He got turned on easily enough when he smelled omega arousal and touched an omega’s soft skin. But he had never been turned on this fiercely before.

“Want to try it out?” Cas’ voice brought him up short.

He reluctantly turned his gaze away from Cas’ pretty little hole and tried to get his brain to cooperate again.

“Didn’t you want to wait till mating?” he asked, proud that he had some brain cells left.

“My _family_ wanted that,” Cas corrected him. “ _I_ really want to see if it fits.”

“Believe me. It’ll fit.”

Cas raised his eyebrows at him. “Prove it.”

There was an omega taunting him, they were both fully aroused and ready to go… Dean’s alpha really wanted to plunge in there and shut that cheeky omega up with a good fucking.

But he held back. Cas’ first time should be special and not a demonstration to teach him where pups came from because he was curious about knots and whether they fit into an omega’s hole. Cas was special and he deserved so much more than some horny alpha taking his virginity because Cas had dared him to.

So, with a heavy heart, Dean’s upstairs brain managed to overrule his downstairs brain.

When he told Cas that they shouldn’t be doing this right now, Cas looked disappointed.

While pulling up his pants, Dean repeated, “It fits,” because that’s what Cas had wanted to know and why he had wanted to experiment around with Dean.

Still, the disappointed frown didn’t vanish from Cas’ face as the omega quickly got dressed again as well.


	2. Chapter 2

Ever since that night, Dean’s alpha hadn’t been interested in so much as looking at other omegas. His mind would sporadically flash back to Cas lying on his back, his finger fucking in and out of himself, slick glistening between his ass cheeks. Plus, the only scent that didn’t make him nauseous was Cas’.

He had known that he was attracted to Cas from the beginning, but he had assumed that it was the whole innocent virgin thing that had piqued the interest of his alpha, who just wanted to pop his cherry and show him the carnal pleasures in life.

But since the developing friendship between Cas and himself had been more important to him than a quick roll in the hay, for once he hadn’t acted on his alpha instincts.

Plus, Cas had just tilted his head and squinted at him when Dean had tried some subtle flirting the first time they’d met.

Now though, it became quite clear that it wasn’t just about deflowering the geeky, naïve omega. Dean had thought about it in the days after they had almost slept together and had come to the conclusion that he didn’t want Cas to see him as a tool to experiment around with, but rather as a potential mate. He could give Cas all the things that he deserved.

With that new realization in mind, he turned their next movie night into a date night, fluffing the pillows, adding that blanket Cas liked to curl up in when he was cold, and generally making his bed as homey as possible.

There. That wasn’t half bad for a nest that was supposed to say, ‘this alpha knows how to provide for his omega.’

Cas, in his usual oblivious fashion, didn’t seem to realize he was being propositioned. He just sank into the pillows, wrapped that cuddly blanket around himself and waited for Dean to start the movie.

Well then. Baby steps.

Dean had chosen a romantic movie to get Cas into a receptive mood, and—oops—he had totally forgotten about that sex scene!

Cue Cas’ questions. “Why is he sinking to his knees?”

“He’s giving him a blowjob,” Dean said, hoping that that would be explanation enough.

Of course, since this wasn’t a porno, you couldn’t really see what was going on, so maybe Cas had just not understood the artistic choice to only show the back of the omega’s head and then cut to the expression of bliss on the alpha’s face.

“A what?”

Dean should have known. Blowjobs were probably considered ‘things of the devil’ too. He paused the movie so that he could explain.

When he had stumbled his way through an explanation about dicks in mouths, Cas punched him lightly in the arm, rolled his eyes, and said, “Ha, ha.”

“Uhm. It’s not supposed to be funny, it’s supposed to be sexy,” Dean informed him, rubbing his arm more for show than anything.

Again with the eye-roll. “That’s not a thing that people do.”

“Uh… Yes, it is.”

Cas looked at him warily, clearly still unbelieving. “You said that in order to make pups, the alpha has to ejaculate into the omega’s ass,” he said, apparently trying to logic him. “How could the alpha impregnate the omega when he is fornicating with his mouth?”

“Sex is supposed to be fun, okay?” Dean said. “Pleasurable. It’s very pleasurable if your partner uses their mouth on you.” There. Try that for logic.

“People put each other’s _penises_ into their _mouths_?” Cas repeated. He seemed to finally realize that Dean wasn’t yanking his chain.

Dean shrugged his shoulders. “It’s not weird,” he said defensively because Cas made it sound like it was some kind of depraved act.

“They _lick_ them and stuff?” Cas asked, repeating what Dean had explained just minutes earlier.

“Yeah. And they have fun doing it,” Dean stressed.

Cas was staring at him all intensely, which was how Dean knew that he was about to ask something ‘of import.’

“Have _you_ done that before?”

“Of course I have. It’s pretty standard,” Dean said and then went on to explain, “You can do it as foreplay, get him all hot and bothered, ready for the main course, or you can get him off with your mouth, swallow his come. If you’re scent-compatible, it tastes _awesome_. If not, it can have a bit of a weird taste, but you might only want to sleep with people you’re scent-compatible with anyway, so…”

“ _We_ are scent-compatible,” Cas interrupted him.

“Uh… yeah… We… yeah.” No question about it. Dean _loved_ Cas’ scent and could totally get lost in it. When their scents mixed after spending a movie night in the same bed, it smelled like the best thing ever.

“So, that means we would like the taste of each other’s ejaculate,” Cas went on.

Dean’s mouth went dry and he had to clear his throat. “You can’t say stuff like that!” he rasped.

“Why not?”

Since Cas was really bad at figuring out innuendo or subtle remarks, Dean decided to be crass. “If you said this to any other alpha, he’d be fucking you by now.”

Cas shot him a meaningful look. Dean half expected him to say, ‘Then what’s wrong with you?’ But instead, the omega was even more forward, “I’ll lick yours if you lick mine.”

Look at him, figuring out how to sixty-nine mere minutes after he had first found out about oral sex.

And how in the world did the virgin omega manage to make Dean all flustered with just a few choice words?! Dean didn’t _get_ flustered about sex! Dean was the one who got _omegas_ to blush and swoon with a wink here and some innuendo there…

This was the second time that Cas had challenged him to an act of intimacy, and surely, a little bit of oral sex wouldn’t hurt. Dean could show Cas how great it could feel, how great Dean could _make_ him feel—which, incidentally, might help convince his omega of what a great choice Dean’s alpha was.

As far as plans for getting an omega to fall for him went, this one seemed a bit risky, but Dean could only say no to Cas asking for sex so many times...


	3. Chapter 3

“Okay,” he said, which seemed to surprise Cas, who quickly proceeded to untangle himself from the blanket he was still wrapped in. Being the geek that he was, he only managed to entangle himself further so that Dean had to help him out, hiding a small smile.

That’s when Dean realized that he would have to guide him and make up the rules, seeing as Cas had never done this before. Rule number one: Kissing was allowed. Encouraged even. So was lots and lots of touching.

As soon as he had Cas out of his shirt, he let his hands roam all over his torso and down to his hips while he was busy nipping at Cas’ lips.

The omega was a bit shy at first, but he quickly got the hang of the teasing give and take of tongue on tongue.

But their tongues were supposed to go to work someplace else, so once the make out session had left them both aroused, Dean slowly proceeded to get them out of the rest of their clothes before he moved them into position.

Finally, they were lying on their sides, facing each other’s stiff pricks.

“Just follow my lead,” Dean instructed and licked along the shaft before taking the head into his mouth and sucking gently.

They were scent-compatible all right. Of course, Dean had known that ever since he had first smelled Cas, but this was scent-compatibility on a whole new level. Dean had never tasted such a delicious cock before. He couldn’t get enough of the smell and taste.

Cas moaned in response. Then he quickly followed suit, and Dean had to suppress a moan of his own. Cas’ tentative flicks of the tongue were better than any expert blowjob Dean had ever received.

From time to time, he had to remind himself that this was the first blowjob Cas had ever given (or received), so he had to hold himself back from delivering a few thrusts and fucking into Cas’ mouth. That was all the more difficult to do since Cas was so responsive and was moaning around his dick constantly, which was such a turn-on that Dean’s alpha was starting to crave more.

He also had to keep himself from deep throating Cas because he was worried the omega might try it as well, which was so not a good idea for a first blowjob.

One of Dean’s hands found its way to Cas’ ass so that he could encourage him to move his hips in rhythm with Dean’s sucking. And since his hand was already there, he pushed a finger between Cas’ cheeks, just to check if he was doing a good job.

There was _a lot_ of slick. Cas was definitely into this.

What was a blowjob without a finger in the omega’s asshole? After all, Dean wanted to show Cas the whole BJ experience. He tongued at the slit of his cock and then laved the tip with his tongue while his hand was fondling his balls.

While Cas was busy whimpering and gently moving his hips back and forth to fuck into Dean’s mouth, Dean pushed one finger into his hole. With so much slick paving the way, it slipped right into the virgin asshole.

God, what a turn-on. No alpha had ever touched Cas there. Dean began fucking Cas with his finger in earnest, spreading his slick against his inner walls and making the omega squirm and moan around Dean’s cock, which in return sent shivers of pleasure up Dean’s spine.

Cas’ scent had turned sweet and desperate, his orgasm clearly approaching. This was the scent of an omega ready to be mounted.

Cas inexpertly but enthusiastically lapping at his dick felt incredible and drove Dean’s alpha wild with lust. That’s when his sex-crazed brain realized: there was no way that Cas would walk away from this without being fucked in the ass.

Dean let Cas’ cock slip from his mouth with a messy slurp and asked, “Do you know how to present?” After all, that would definitely be the easiest position for a first time taking an alpha cock.

Cas stopped sucking Dean too and shook his head.

“Want me to show you?”

Cas nodded eagerly and got onto his hands and knees. Dean helped him get into the right position, and then moved behind him, ready to push the head of his cock against Cas’ entrance.

“This okay?” he asked, holding his alpha back to make sure that this was what Cas wanted too, even though the omega was the one who had teased and propositioned his alpha to the point of no return.

“Yes, Dean! Please!”

That was all the encouragement Dean needed to carefully enter the omega. This was the moment. Cas was taking an alpha cock for the very first time. And he looked so beautiful doing it! No omega presenting his ass for the taking had ever looked so… debauchable.

A few thrusts got Dean halfway into the tight channel before he paused to give Cas’ virgin ass some time to get used to the new feeling of having an alpha cock breach him. Even though Cas’ channel was oh-so tight, the omega’s slick paved the way for his rather sizeable erection, and then Dean finally bottomed out and he had to close his eyes in ecstasy.

Feeling Cas’ inner walls stretch around his intrusion to accommodate his huge erection just felt too good.

After a while, he experimentally moved around, using short thrusts until he had located Cas’ prostate. The omega whimpered and all Dean could do was grunt in response.

Then he proceeded to fuck Cas gently, wanting to make him feel loved and cherished. Even though his alpha wanted to assert his claim on this omega and drill him into submission, Dean made sure that Cas’ hole wouldn’t get a rough pounding this first time.

Instead, he reached around to play with Cas’ cock a bit, and when Cas mewled, “Dean!” half pleasure, half frustration, he finally gave him the friction he really needed, tugging on his little omega prick until Cas came all over the sheets—for the first time brought to orgasm by the hands of an alpha.

Dean’s knot was slapping against Cas’ ass, trying to get in, but Dean didn’t want to stretch Cas past the point he was comfortable with, so he just delivered two, three harsher thrusts to get himself over the edge and then flooded the omega’s ass with his sperm.

After his dick was done squirting its juice into the asshole, he collapsed on top of Cas, who sank down into the mattress, unable to hold the position any longer.

Dean placed a loving kiss to the back of Cas’ neck.

This omega was not a virgin anymore. He had a huge load of Dean’s spunk inside of him to prove it. That thought alone made Dean’s dick twitch.

Cas turned around, dislodging Dean’s cock from his ass in the process. Once he was lying on his back, he took hold of Dean’s dick again to get it back into his ass, pushing against Dean harshly. This surprised Dean into a thrust of his own that pushed the knot into Cas’ channel, effectively locking them together.

Of course, his knot liked that feeling and Dean’s dick shot off again, adding to the load of spunk in Cas’ hole, filling him up good.

“Ungh!” Dean grunted, pressing himself close to Cas so that everything he had left to give would end up deep inside of the omega. Cas’ womb had just received the first load of alpha sperm and even though Cas wasn’t in heat and this had clearly fallen in the ‘sex for pleasure’ category, the thought of Dean’s guys in there searching for an egg to fertilize was kind of hot.

Cas blinked up at him and smiled shyly. “It does fit,” he said, letting his eyes drop to the place where they were joined by Dean’s knot, a grin playing around his kiss-swollen lips.

“Told ya,” Dean replied before he swooped down to steal another taste of those delicious lips.

“I _really_ like blowjobs,” Cas said when Dean moved on from his lips to kiss down his neck.

Dean stopped peppering him with kisses to look at him. “Yeah—you realize that that was more than a blowjob, right?” he asked, and he couldn’t believe that that wasn’t even a teasing question but a real one.

Cas rolled his eyes. Good. Apparently, Dean had explained the mechanics of sex well enough so that Cas had known what was going on.

“I really like getting fucked as well,” Cas reassured Dean.

Hearing Cas say ‘getting fucked’ awakened his alpha again and his dick, which had made itself comfortable in Cas’ warmth, twitched once more. Damn, this omega was like Viagra.

“So…” Dean said, remembering what had started all of this. He tried to be casual about it, even though he was a bit mad at himself that he had jumped Cas before he’d had a chance to prove to the omega what a great choice as a mate he’d make. “The experiment was successful, huh?”

Cas tilted his head. “What experiment?”

“You know… trying out sex.” Dean was very aware of the fact that they were still lying in each other’s arms, naked, Dean’s cock inside Cas’ hole. Maybe this wasn’t the best time to be having this conversation.

“Ouch!” he said when Cas flicked his arm. “What was that for?!”

“This wasn’t an experiment for me, assbutt.” Cas glowered at him. “I was propositioning you.”

“Yeah, I got that. For sex.”

There was a beat of silence. Then Cas asked, “Is that what you think this is?”

A flicker of hope blossomed in his chest. “You don’t?”

“You made a nest for me,” Cas pointed out, motioning at the fluffy sheets around them. “And then you showed me a sex movie.” He pointed at the television that was still paused at the blowjob scene that had started it all.

“That was _not_ a sex movie!” Dean spluttered. “That was _one_ scene. A scene I had forgotten all about!”

That brought Cas up short. “So, that wasn’t your way of telling me that you want me?” he asked, unsure.

“Oh, no, it definitely was. I mean, not the sex movie—which, again, not a sex movie—but… yeah, I… y’know… want you.”

“Good.” Cas snuggled up to him. “’Cause I believe in mating for life.”

Mating? Dean perked up at that. Yeah, his nest had totally given the message that he was a reliable alpha who was a good candidate for mating purposes.

Satisfied that he had managed to score this amazing omega with the help of his awesome nest-building skills, Dean began licking at Cas’ mating gland. He couldn’t wait to teach this omega some more about sex positions and how an alpha and an omega could make each other feel good. He also couldn’t wait to place a mating bite on him.

Till then, a love bite would have to do.

**Author's Note:**

> I hope you liked it and if you did, I’d love to chat with you in the comment section. ❤️ ❤️ ❤️
> 
> Also, if you want to support me another way: Since I'm a no-name fan on tumblr, it would help me out if you'd **[reblog this fanfic (click here for the tumblr link)](https://destielshipper4cas.tumblr.com/post/190325977544/sex-ed-finished-rating-explicit-tags-omega)**.


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